The problem seems to be related to guest screen geometry; at one point I shutdown my windows vm in windowed mode and then relaunched it, switching to full-screen when the windows logo appeared. At that point, while the VM still showed a screen that was vertically smaller than the actual screen allocated, I was able to mouse to the bottom of the VMs drawn screen and get the toolbar to pop-out.

However, once the guest additions loaded and expanded the guest's screen to the full footprint, I was no longer able to get the toolbar to pop-out.

Interestingly, the mini-toolbar remnant (the one or two pixel tell-tale that persists) is visible, especially in Ubuntu 12.04 where the bottom of the guest's screen is dark and otherwise empty.